The march of Cato from Berenice, in the province of Cyrene, was much longer than that of Heraclius from Tripoli. He passed the deep sandy desert in thirty days, and it was found necessary to provide, besides the ordinary supplies, a great number of skins filled with water, and several Psylli, who were supposed to possess the art of sucking the wounds which had been made by the serpents of their native country. See Plutarch in Caton. Uticens. [c. 56] tom. iv. p. 275; Strabon. Geograph. 1. xvii. p. 1193 [p. 836, ed. Casaub.].